This invention relates to a self-advancing film cassette for advancing the leader of a photographic film strip through a film passage mouth of the cassette in accordance with rotation of a spool.
Presently, a photographic film cassette containing a roll of photographic film strip of 135 type (35 mm in width) is most widely used. This photographic film cassette is constituted by a light tight cylindrical cassette housing provided with a film passage mouth, a spool rotatably contained in the cassette housing, and a roll of film coiled on the spool. The leader of the film protrudes outside through the film passage mouth. When loading the film cassette in a camera, the film leader is brought into engagement with a threading member of the camera. By driving the threading member, the film is pulled out from the cassette housing and is fed to a film take-up chamber so as to be wound on a take-up spool in this chamber.
In recent years, in order to make the photographic film cassette compact and easy to handle, a self-advancing film cassette has been proposed in which the entire film is contained in the cassette housing, and the film leader is advanced from the film passage mouth in accordance with rotation of the spool. In order to advance the film leader reliably, it is necessary for this kind of film cassette to rotate the spool integrally with the roll of film, thereby to transmit the rotation of the spool to the film leader reliably. For example, in Japanese Patent Laid-open Publication No. Sho 53-13918, a self-advancing film cassette is described, in which both sides of a film trailer and a spool shaft are provided with teeth. By meshing with these teeth, the spool and the roll of film are rotated integrally. On the other hand, in Japanese Utility Model Laid-open Publication No. Sho 62-164343, another self-advancing film cassette is described, in which a spool is provided on its outer surface with a substance having a shock absorbing property and resilience in order to increase friction between the spool and the film.
If the roll of film is partially loosened, a part of the film is reversed and is bent in a generally U-shape. In U.S. Pat. No. 4,832,275, a self-advancing film cassette is described, in which a pair of rings are disposed around both ends of a roll of film wound on a spool. Further, in U.S. Pat. No(s). 4,834,306 and 4,848,693 a self-advancing film cassette is described, in which a rim is provided on flanges of a spool in order to press both sides of the outermost turn of a roll of film with the rim. In U.S. Pat. No. 4,846,418, a construction is described in which a spool is formed of a pair of spool halves which are slidable in an axial direction, and both sides of a roll of film are clamped by the pair of spool halves.
However, when both sides of the film trailer and the spool shaft are provided with teeth there arises a problem in that the configurations of the film and the spool become complicated, and manufacturing costs become high. Although all the other self-advancing film cassettes mentioned above have such an advantage that the loosening of the peripheral portion of the roll of film can be prevented, a space is likely to be formed in the vicinity of a shaft of the spool because of loosening of the roll of film. If this space is formed, the film is likely to be reversed in a U-shape when the spool rotates in the unwinding direction. This causes the film to jam and makes it impossible to advance the film leader.